Both parts of your commit seem to have helped. However I found two failures still happening, and one new failure:

1. Casablanca and El_Aaiun still failing since the original commit:
http://buildbot.python.org/all/builders/PPC64%20Fedora%203.x/builds/1318/steps/test/logs/stdio
======================================================================
FAIL: test_system_transitions (test.datetimetester.ZoneInfoTest[Africa/El_Aaiun])
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/shager/cpython-buildarea/3.x.edelsohn-fedora-ppc64/build/Lib/test/datetimetester.py", line 4781, in test_system_transitions
    self.assertEquivDatetimes(sdt, tzdt)
  File "/home/shager/cpython-buildarea/3.x.edelsohn-fedora-ppc64/build/Lib/test/datetimetester.py", line 4706, in assertEquivDatetimes
    (b.replace(tzinfo=None), b.fold, id(b.tzinfo)))
AssertionError: Tuples differ: (datetime.datetime(2037, 10, 10, 3, 0), 0, 271733936) != (datetime.datetime(2037, 10, 10, 2, 0, fold=1), 1, 271733936)

First differing element 0:
datetime.datetime(2037, 10, 10, 3, 0)
datetime.datetime(2037, 10, 10, 2, 0, fold=1)

- (datetime.datetime(2037, 10, 10, 3, 0), 0, 271733936)
?                                  ^      ^

+ (datetime.datetime(2037, 10, 10, 2, 0, fold=1), 1, 271733936)
?                                  ^   ++++++++   ^

2. The two Gentoo buildbots started failing at some point _after_ the original commit. The corresponding commit (b04560c3ce69) is not relevant to datetime.
http://buildbot.python.org/all/builders/x86%20Gentoo%20Non-Debug%20with%20X%203.x/builds/1219/steps/test/logs/stdio
======================================================================
ERROR: test_folds (test.datetimetester.ZoneInfoTest[Asia/Qyzylorda])
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/buildbot/buildarea/3.x.ware-gentoo-x86/build/Lib/test/datetimetester.py", line 4694, in setUp
    self.tz = ZoneInfo.fromname(self.zonename)
  File "/buildbot/buildarea/3.x.ware-gentoo-x86/build/Lib/test/datetimetester.py", line 4527, in fromname
    return cls.fromfile(f)
  File "/buildbot/buildarea/3.x.ware-gentoo-x86/build/Lib/test/datetimetester.py", line 4519, in fromfile
    self = cls(ut, ti)
  File "/buildbot/buildarea/3.x.ware-gentoo-x86/build/Lib/test/datetimetester.py", line 4472, in __init__
    self.lt = self.invert(ut, ti)
  File "/buildbot/buildarea/3.x.ware-gentoo-x86/build/Lib/test/datetimetester.py", line 4482, in invert
    lt[0][i] += ti[i-1][0] // SEC
OverflowError: Python int too large to convert to C long

3. It looks like removing the sizeof_time_t skip re-introduced a year 2037 failure for Cairo, although many other tests (e.g. New_York) that were skipped are now passing:
http://buildbot.python.org/all/builders/x86%20Gentoo%20Non-Debug%20with%20X%203.x/builds/1228/steps/test/logs/stdio
======================================================================
FAIL: test_system_transitions (test.datetimetester.ZoneInfoTest[Africa/Cairo])
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/buildbot/buildarea/3.x.ware-gentoo-x86/build/Lib/test/datetimetester.py", line 4781, in test_system_transitions
    self.assertEquivDatetimes(sdt, tzdt)
  File "/buildbot/buildarea/3.x.ware-gentoo-x86/build/Lib/test/datetimetester.py", line 4706, in assertEquivDatetimes
    (b.replace(tzinfo=None), b.fold, id(b.tzinfo)))
AssertionError: Tuples differ: (datetime.datetime(2037, 10, 9, 0, 0), 0, 137328448) != (datetime.datetime(2037, 10, 8, 23, 0, fold=1), 1, 137328448)

First differing element 0:
datetime.datetime(2037, 10, 9, 0, 0)
datetime.datetime(2037, 10, 8, 23, 0, fold=1)

- (datetime.datetime(2037, 10, 9, 0, 0), 0, 137328448)
?                              ^     ^   ^

+ (datetime.datetime(2037, 10, 8, 23, 0, fold=1), 1, 137328448)
?                              ^ ++++    ^^^^^^   ^